I recently installed the Borla S-Type cat back which is the loud version. I've heard others mention some of the aftermarket exhaust are too quiet which is why I went with the S-Type. I can actually hear the exhaust when I get on it but subtle from inside when cruising.
I also went with a Diablo i3 tuner from Diablew as it was the most affordable combo (tuner + custom tunes) I could find at $500 and a friend was happy with his GMC truck tune from them. The process was simple and Lew at Diablew provides excellent communication. You can have the base tune installed with custom tune within a few days. Keep in mind 150 miles is required between each of the base, custom, and WOT tunes. Log files need to be sent back between each tune to ensure the custom tunes meet the conditions for your geographic location and gas quality.
Adding just the catback will result in a mechanical knock that I've been told is the Displacement on Demand switching between 4 and 8 cylinders and is very annoying. The custom tune can remove the DOD and resolves the racket and will improve performance as it will always run 8cyl. I have a 2016 Escalade so I was able to have my trans tuned as well and the driving characteristics with the ECM tune make for an awesome total package. Very happy with my decision.
At that kind of money isnt the AutoCal from BB a better option?